A power supply controller, in which a high-power semiconductor switching element such as a power MOSFET is disposed on a current supply line connected between a power source and a load, is conventionally provided. The power supply to the load is controlled by switching the semiconductor switching element between ON and OFF. In such a power supply controller, it is known that a self-protective function is provided for protecting its own switching element described above by controlling the potential of the control terminal of the semiconductor switching element so as to turn off the switching element in response to an occurrence of overcurrent. Specifically, as shown in JP-A-2001-217696, a current detecting resistor is serially connected to the load terminal (e.g., the source or drain in the case of a MOSFET). The voltage drop in the resistor is detected, and the occurrence of overcurrent is determined if the voltage drop is larger than a predetermined level.
The current blocking due to the above-described self-protective function is automatically restored, that is, the switching element is turned on again, when a predetermined time has elapsed after the blocking. This is because the function is provided to prevent the semiconductor switching element itself from overheating and, when the abnormal current is blocked, the temperature of the semiconductor switching element should be immediately lowered by a heat radiator conventionally provided therein.
For example, in case that short-circuiting has occurred in an external circuit, i.e., a load of the power supply controller, the above means that an ON-OFF operation, in which the semiconductor switching element is immediately tuned off in response to the short-circuiting current and thereafter turned on when the predetermined time has elapsed, is repeated. According to this, the semiconductor switching element is likely to overheat and thereby damaged depending on the radiating characteristics, or an electric wire or the like in the external circuit connected to this power supply controller may be burnt out. Therefore a fuse element is conventionally provided in the external circuit in consideration of its resistance and thermal property, and the circuit is generally disconnected by burning out the fuse element at the time of occurrence of short-circuiting current or the like so as not to be automatically restored.
However, the additionally provided fuse element results in an overall larger device. Thus, the problem arises that the above device fails to meet the recently growing demand of miniaturization of the device or integration in the circuit construction.
The present invention was made in view of the foregoing circumstances, and an object thereof is to provide a power supply controller capable of protecting an external circuit utilizing the self-protective function of a semiconductor switching element.